Audio rendering system

ABSTRACT

An audio rendering device includes: at least one wireless communications interface configured to receive a first plurality of audio packets from a wireless communication device, the first plurality of audio packets including frames of audio data for a first audio channel from a set of one or more audio channels; and a processing unit; wherein the audio rendering device is configured to release, at respective first buffer release times, the frames of the audio data for the first audio channel from a first buffer for rendering by the processing unit; wherein the audio rendering device is configured to receive one or more messages from an other audio rendering device; and wherein the audio rendering device is configured to synchronize the first buffer release times with second buffer release times associated with the other audio rendering device based on the received one or more messages.

RELATED APPLICATION DATA

This application is a continuation of U.S. Pat. Application No.17/143,103 filed on Jan. 6, 2021, pending, which is a continuation ofU.S. Pat. Application No. 16/450,545, filed on Jun. 24, 2019, now U.S.Pat. No. 10,904,666, which claims priority to, and the benefit of,Danish Patent Application No. PA 2018 70518 filed on Aug. 7, 2018, andEuropean Patent Application No. 18189208.4 filed on Aug. 15, 2018. Theentire disclosures of the above applications are expressly incorporatedby reference herein.

FIELD

The present disclosure relates to an audio rendering system comprising awireless communications device, a first audio rendering device and asecond audio rendering device. In particular, the present disclosurerelates to such a system wherein the wireless communications device isconfigured to transmit a first plurality of audio packets to the firstaudio rendering device and a second plurality of audio packets to thesecond audio rendering device, the first plurality of audio packetsincluding audio data for a first audio channel from a set of one or moreaudio channels and the second plurality of audio packets including audiodata for a second audio channel from said set of one or more audiochannels. The present disclosure relates to further aspects related tosuch a system.

BACKGROUND

Wireless streaming of audio data by a pair of audio rendering devicesfrom a wireless communications device is highly desirable. There exist,however, a number of technical problems in terms of power consumption,reliability, transmission latency and/or delay, component size etc. withprior art wireless data communication methodologies, protocols anddevices that must be addressed to deliver a feasible solution for anaudio rendering device. These challenges are particularly pronouncedwhen the audio rendering device has a small form factor and/or only asmall amount of power available. In particular, this is the case whenthe pair of audio rendering devices form a pair of hearing instruments.

Standardized wireless data communication protocols such as Bluetooth LE(BLE) as defined by the Bluetooth Core Specification 5.0, or earlierversions, does not allow for real-time audio transport.

The lack of real-time transport means also means that stereosynchronization between two paired audio sinks (such as hearing aids) isdifficult to achieve.

US 9,712,266 discloses techniques for synchronizing rendering ofmulti-channel audio output where the wireless communications devicewirelessly transmits an indication to one of the audio rendering devicesto delay rendering audio data by a certain length of time.

However, this solution requires modification of the wirelesscommunications device. Therefore it may be desirable to provide a systemthat does not require specific modifications or configuration of thewireless communications device. In particular it may be desirable toprovide a system that allows use of an existing wireless communicationsdevice as part of the system and/or that provides larger flexibility asto the choice of wireless communications device.

It is generally desirable to overcome one or more of the above-mentionedproblems and shortcomings of the prior art wireless data communicationmethodologies, protocols and devices and or to provide an alternativethereto.

SUMMARY

According to a first aspect, disclosed herein are embodiments of anaudio rendering system; comprising a wireless communications device, afirst audio rendering device and a second audio rendering device. Thewireless communications device is configured to transmit a firstplurality of audio packets to the first audio rendering device and totransmit a second plurality of audio packets to the second audiorendering device, the first plurality of audio packets including framesof audio data for a first audio channel from a set of one or more audiochannels and the second plurality of audio packets including frames ofaudio data for a second audio channel from said set of one or more audiochannels. The first audio rendering device is configured to maintain afirst buffer of received frames of audio data for the first audiochannel and to release, at respective first buffer release times, framesof audio data for the first audio channel from said first buffer forrendering. The second audio rendering device is configured to maintain asecond buffer of received frames of audio data for the second audiochannel and to release, at respective second buffer release times,frames of audio data for the second audio channel from said secondbuffer for rendering. The first audio rendering device is configured toreceive one or more messages from the second audio rendering device.Moreover, at least the first audio rendering device is configured tosynchronise the first buffer release times with the second bufferrelease times based on the received one or more messages.

Accordingly, by introducing respective buffers at the first and secondaudio rendering devices and by synchronising, based on communicationbetween the first and second audio rendering device, release times forreleasing frames from the buffers, an efficient system for renderingaudio content on two devices in a synchronised manner is provided.

As the synchronisation is based on communication between the audiorendering devices, the synchronisation is not dependent on specificsynchronisation information from the wireless communications device.Accordingly, the wireless communication device does not need to becapable of providing such information.

Moreover, the provision of respective buffers at the audio renderingdevices and by synchronising buffer release times, the synchronisedrendering is robust against unreliable communication between thewireless communications device and the respective audio renderingdevices. In particular, the system may account for failures in audiopacket transmission on the individual communications channels whilemaintaining synchronised audio rendering at least to a large degree.

The audio data may be for stereo audio output that includes a pluralityof stereo audio channels. The first and second audio channels may thusbe different audio channels, e.g. a left and right stereo audio channel,respectively. In some embodiments the first and second audio channelsmay be the same channel which is intended for synchronised rendering viamultiple audio rendering devices.

The audio data may comprise a plurality of samples or values of adigital audio signal, such as a sequence of discrete-time anddiscrete-amplitude digital audio signal values that representcontinuous-time and continuous-amplitude values of an analogue audiosignal that can be converted into acoustic sound. The audio samples orvalues may be arranged in frames of fixed or variable length. The audiodata may be encoded audio data, i.e. the audio data may be received inencoded form. In other words, the audio data and frames may containencoded digital data that are intended for conversion into sound by theaudio rendering device as is well-known in the art of streaming audio.For the purpose of the present description, the conversion of the audiodata into sound is also referred to as rendering. The conversion mayinclude several processing steps, e.g. including a decoding step whenthe audio data is encoded according to a suitable encoding scheme.Hence, the term audio data is intended to encompass encoded audio dataand non-encoded/decoded audio data.

According to some embodiments, the wireless communications channelbetween the wireless communications device and each of the audiorendering devices and/or the communications channel between the firstand second audio rendering devices may utilise radio-frequencycommunication, e.g. using one or more frequency bands located in theindustrial scientific medical (ISM) radio frequency range such as in the2.40-2.50 GHz band or the 902-928 MHz band. The wireless communicationmay alternatively use another suitable frequency band. In someembodiments, the wireless communications between the wirelesscommunications device and each of the audio rendering devices and thewireless communications between the first and second audio renderingdevices may utilise the same frequency band or respective frequencybands.

The wireless communications device may be configured to transmit thefirst plurality of audio packets to the first audio rendering device viaa first wireless communications link between the wireless communicationsdevice and the first audio rendering device, in particular via a directwireless communications link, or otherwise via a wireless communicationslink not involving the second audio rendering device. The wirelesscommunications device may be configured to operate as a master deviceand the first audio rendering device may be configured to operate as afirst slave device when communicating data between the wirelesscommunications device and the first audio rendering device, e.g. underan audio-enabled Bluetooth LE protocol or under another suitablecommunications protocol for communicating audio data.

Similarly, the wireless communications device may be configured totransmit the second plurality of audio packets to the second audiorendering device via a second wireless communications link between thewireless communications device and the second audio rendering device, inparticular via a direct wireless communications link, or otherwise via awireless communications link not involving the first audio renderingdevice. The wireless communications device may be configured to operateas a master device and the second audio rendering device may beconfigured to operate as a second slave device when communicating databetween the wireless communications device and the second audiorendering device, e.g. under an audio-enabled Bluetooth LE protocol orunder another suitable communications protocol for communicating audiodata.

In some embodiments, each of the audio rendering devices may compriseone or more hardware components that implement the communication withthe wireless communications device as well as the communication with theother audio rendering device. This may be particularly feasible andadvantageous when the wireless communications between the wirelesscommunications device and the respective audio rendering devices usesthe same general communications technology as the wireless communicationbetween the first audio rendering device and the second audio renderingdevice. In particular, the respective communications channels may use RFcommunication using the same or similar frequency bands and/or sharingthe same or similar implementations of at least some layers of thecommunications stack, e.g. the lowest one or more layers of thecommunications stack. For example, the audio rendering device mayinclude a single antenna and/or a single transceiver and/or the samecommunications controller, thus allowing the audio rendering device tomaintain a small form factor.

In some embodiments, the wireless communications device may communicatethe audio packets to the respective audio rendering devices usingBluetooth communication, such as Bluetooth LE communication.

In some embodiments, the wireless communications channel between thefirst and second audio rendering devices may be based on near-fieldmagnetic coupling between inductive coils of the first and second audiorendering devices. In the latter embodiment, the plurality of spacedapart frequency bands may be arranged in a radio frequency range below 2GHz, for example below 1 GHz, or below 500 MHz.

The communication between the first and second audio rendering devicesmay be unidirectional or bidirectional. The communication may bewireless, e.g. using radio-frequency communication, inductivecommunication or the like. The communications may be direct or indirect.The communication may be in the form of data packets. The communicationmay convey messages including control data. In particular, the messagesexchanged between the first and second audio rendering devices on whichsynchronisation is performed as described herein may lack audio data.The messages may thus solely include one or more types of control datafor the aligning or synchronization of the operation of the first andsecond audio rendering devices as discussed in further detail herein.Alternatively, at least some of the data communicated between the firstand second audio rendering devices may comprise audio data and/orcontrol data used for purposes other than synchronizing the rendering ofaudio channels. The communications between the first and second audiorendering devices may be via a communications link separate and distinctfrom the first communications links used for communicating the firstplurality of audio packets from the wireless communications device tothe first audio rendering device and separate and distinct from thesecond communications links used for communicating the second pluralityof audio packets from the wireless communications device to the secondaudio rendering device. Accordingly, neither the first nor secondplurality of audio packets need to be communicated between the first andsecond audio rendering devices.

The first and second audio rendering devices may maintain acommunication link with each other over an extended period of time.Alternatively, they may intermittently establish communications linksduring each of a plurality of successive connection events while beingcommunicatively disconnected during intervening idle time periods.Hence, the plurality of consecutive connection events may be separatedby intervening disconnect or idle time periods without data exchangebetween the first and second audio rendering devices. Hence, each pairof successive connection events may be separated by a disconnect periodor idle time period. Similarly, even when the first and second audiorendering devices maintain a communication link, the first and secondaudio rendering devices may communicate data over the communicationslink at successive communication events separated by idle times. Thetime separation, or transmission interval, between a pair of adjacentconnection or communication events may be between 5 ms and 500 ms suchas between 10 ms and 200 ms, such as between 10 ms and 100 ms. The timeseparation, or transmission interval, may be fixed or vary over time,e.g. responsive to available bandwidth and/or transmission of higherpriority data. In some embodiments, at each connection or communicationevent, a message from one of the audio rendering device to the otheraudio rendering device is sent without communicating a message in thereverse direction. At a subsequent communication or connection event, amessage may be sent in the reverse direction, i.e. such that, at anygiven communication or connection event, each device either onlyreceives or transmits a message. The sending and receiving roles maythen be reversed at alternating connection or communication events. Itwill be appreciated, however, that other embodiments may use othercommunications protocols. The messages may be communicated as datapackets according to a suitable communications protocol.

The wireless communications device may transmit audio packets to therespective audio rendering devices according to a transmission schedule.In particular, the wireless communication device may transmit audiopackets to the first audio rendering device at regularly spaced apartcommunication events, i.e. the audio packets of the first plurality ofaudio packets are sent at equal time intervals between subsequenttransmissions. Similarly, the wireless communication device may transmitaudio packets to the second audio rendering device at regularly spacedapart communication events, i.e. the audio packets of the secondplurality of audio packets are sent at equal time intervals betweensubsequent transmissions. The time intervals between transmissions maybe the same for both channels.

The communication between each of the first and second audio renderingdevices and the wireless communications device may be bi-directional. Inparticular, in some embodiments, the first and second audio renderingdevices may be configured to transmit respective acknowledgementmessages to the wireless communications device responsive to successfulreceipt of each of the first or second plurality of audio packets. Tothis end, each of the first and second pluralities of audio packets maycomprise suitable data check sections comprising a packeterror-detection and/or packet error-correction code. The packeterror-detection and/or error-correction code may for example comprise acyclic redundancy check (CRC) code.

In some embodiments, the wireless communications device may beconfigured to retransmit audio packets for which the wirelesscommunications device has not received an acknowledgement of successfulreceipt from the corresponding audio rendering device. In someembodiments, retransmission is carried out until an acknowledgement ofsuccessful receipt is received. In some embodiments, however,retransmission is only repeated for a maximum of N times, N being apositive integer. If N retransmissions have been reached, and thewireless communication device has still not received an acknowledgementindicator indicative of a successful receipt of the audio packet by thecorresponding audio rendering device, the wireless communications devicemay proceed to flush, delete or abandon the audio packet since N failedretransmissions have now been carried out or even completely reset thecommunications link. Alternatively, if the N retransmissions have notbeen reached, the wireless communications device may make a furtherretransmission attempt of the audio packet and thereafter proceed tomonitor the wireless communication channel awaiting an acknowledgmentindicator from the corresponding audio rendering device to which theaudio packet has been sent. Generally, upon receipt of anacknowledgement indicator indicative of successful receipt of the audiopacket by the audio rendering device to which the audio packet has beensent, the wireless communications device may proceed by transmittinganother audio packet according to the transmission schedule. In someembodiments, the wireless communications device may skip one or moresubsequent audio packets, and proceed with a later audio packet of thesequence, when transmission of a previous audio packet has been undulydelayed, e.g. due to a high number of retransmissions. For example, ifaudio packet K was retransmitted multiple times before anacknowledgement of successful receipt has been received, the wirelesscommunication device may proceed by transmitting audio packet K+ 1 + k(k being a positive integer) instead of audio packet K+1.

The flushing of the failed audio packet and/or of a subsequent, not yettransmitted audio packet, allows the wireless communications device toproceed with a more up-to-date or current audio frame. This flushingprocedure in respect of lost or delayed audio packets avoids that audiotransmission through the wireless communications channel is blocked orhung by a large number, in principle an infinite number, ofretransmission attempts of a particular audio packet. Alternatively toflushing audio packets, some embodiments may reset the entirecommunications link when the number of retransmissions exceeds a maximumnumber if transmission attempts.

The provision of frame buffers at the respective audio rendering devicesallows for an efficient synchronisation of the audio channels. The firstand/or second buffer may be a frame buffer configured to buffer audiodata in units of frames. In some embodiments, each received audio packetincludes a single frame. In other embodiments some or all audio packetsmay include more than one frame. It will be appreciated that the audiorendering device may buffer the received audio data in encoded form,e.g. as received from the wireless communications device. In otherembodiments, the audio rendering device may process the received audiodata before buffering it. For example, when the audio data is receivedby the audio rendering device as encoded audio data, the audio renderingdevice may buffer the audio data in encoded form or it may initiallydecode the encoded audio data and buffer the audio data in decoded form.Buffering the audio data in encoded form typically reduces the requiredsize of the buffer. Buffering the audio data after decoding may reducethe latency of the rendering steps of frames that have been releasedfrom the buffer. Generally, the audio rendering device may, in someembodiments, process the received audio data before buffering it while,in other embodiments, the audio rendering device may buffer the receivedaudio data without prior processing.

The buffer may be configured to hold multiple frames. When the audiorendering device receives a new frame of audio data, the received frameof audio data is placed in the buffer. The audio rendering device isfurther configured to release the oldest frame of audio data forrendering, e.g. to a signal processing circuit that is configured todecode the frame of audio data so as to create an audio signal that canbe forwarded to a output transducer. The audio rendering device may beconfigured to release frames of audio data from the buffer at bufferrelease times which may be regularly spaced apart, e.g. spaced apart byan interval that corresponds to the duration of an audio signal encodedby one frame of audio data. It is generally preferred that the firstbuffer release times are regularly spaced apart by a first interval andwherein the second buffer release times are regularly spaced apart by asecond interval equal to the first interval. To this end, the audiorendering device may cause release of the oldest frame of audio data inthe buffer responsive to the receipt of a new frame of audio data whichis then placed in the buffer. Hence, the buffer release times may bedetermined from the times of receipt of the audio packets form thewireless communications device, which in turn is determined by thetransmission schedule of the wireless communications device and anylatencies of the transmission.

In particular, in some embodiments, the wireless communications deviceis configured to transmit the first plurality of audio packets and thesecond plurality of audio packets according to a transmission schedule,such that audio packets of the first plurality of audio packets arescheduled for transmission to the first audio rendering device and thateach audio packet of the second plurality of audio packets is scheduledfor transmission to the second audio rendering device at a delayinterval after the corresponding audio packet of the first plurality ofaudio packets is scheduled for transmission; and wherein at least thefirst audio rendering device is configured to determine the delayinterval based on at least one of the exchanged messages.

For example, the time interval between transmissions of consecutiveaudio packets to each of the audio rendering device may be between 10 msand 20 ms. The delay between transmission of an audio packet to one ofthe audio rendering devices and the transmission of a correspondingaudio packet to the other audio rendering device may be between 1 ms andup to the length of the time interval, e.g. up to between 10 ms and 20ms.

Accordingly, when the audio packets are transmitted to the respectiveaudio rendering devices at regular intervals and such that the intervallength is the same for both audio rendering devices, the audio renderingdevices also release frames from their respective buffers at regularlyspaced apart release times where the buffer release times are spacedapart by the same interval for both audio rendering devices, thusfacilitating synchronisation of the audio channels.

Moreover when the audio rendering devices determine, based on messagescommunicated between the audio rendering devices, the relative delay ofthe transmission of the audio packets to the first and second audiorendering device respectively, proper synchronisation may be performedwithout the need for additional scheduling information from the wirelesscommunications. Moreover, the synchronisation requires only smallamounts of data to be exchanged between the audio rendering devices.

Accordingly, in some embodiments, the first audio rendering device isconfigured to:

-   determine first packet receipt times indicative of respective times    of receipt of audio packets of the first plurality of audio packets    from the wireless communications device; and to-   determine the first buffer release times from the determined first    packet receipt times and from the delay interval.

In one embodiment, the first audio rendering device is configured torelease audio packets from the first buffer at the determined packetreceipt times delayed by a buffer release delay configured to compensatefor one or more delays, including for said delay interval.

It will be appreciated that the second audio rendering device mayperform a corresponding process when the transmission of audio packetsto the first audio rendering device is delayed relative to thetransmission of corresponding audio packets to the second audiorendering device. In any event, the audio rendering device that receivesthe audio packets later than the other audio rendering device receivesthe corresponding audio packets does not need to further delay releaseof audio frames from its buffer relative to the time of receipt of newaudio frames in order to compensate for the relative delay intransmissions by the wireless communications device.

In some embodiments, at least the first audio rendering device isconfigured to receive a message from the second audio rendering deviceindicative of a time of receipt, by the second audio rendering device,of a previous one of the second plurality of audio packets; and todetermine the delay interval from the received message and from a timeof receipt of a previous one of the first plurality of audio packets bythe first audio rendering device. Accordingly, the first audio renderingdevice may efficiently determine the applicable delay without the needfor large amounts of data to be exchanged between the audio renderingdevices. For example, there is no need for a synchronisation of internalclocks of the respective audio rendering devices. Moreover, as thetransmission delay is generally constant during a communicationssession, it may be sufficient to perform the determination of the delayinterval only at the beginning of the communications session, e.g. basedon the initial audio packets. Nevertheless, in some embodiments, thedetermination of the delay interval may be repeated, e.g. periodically,during the communications session. It will further be appreciated that,in some embodiments, both audio rendering devices receive one or moremessages from the corresponding other audio rendering device, e.g.messages indicative of a time of receipt, by the corresponding otheraudio rendering device, of a previous one of the corresponding pluralityof audio packets. Accordingly, the devices may determine which of thetwo devices receives the audio packets delayed relative to the otheraudio rendering device.

However, it will be appreciated that one or both audio rendering devicesmay add additional or alternative buffer release delays in order tocompensate for other latency factors.

As discussed above, in some embodiments, the wireless communicationsdevice is configured to retransmit an audio packet responsive to failureto receipt an acknowledgement indication from the corresponding audiorendering device indicative of successful receipt. It will beappreciated that such retransmission, in particular if multipleretransmissions occur for an audio packet, may cause transmission ofsubsequent audio packets to be delayed. Such delays may be accommodatedby the receiving audio rendering device by means of the buffer. In someembodiments, the wireless communications device may be configured totransmit more than one audio packet at a subsequent scheduledtransmission time and/or transmit additional audio packets betweenscheduled transmission times so as to allow the receiving audiorendering device to replenish its buffer.

Generally the frames of audio data are configured for synchronisedrendering. To this end, for each frame of audio data for the secondaudio channel, the frames of audio data for the first audio channel maycomprise a corresponding frame of audio data, such that the audio datain the frame for the second audio channel and audio data in thecorresponding frame for the first audio channel are configured forsimultaneous rendering as part of, respectively, the first audio channeland the second audio channel. In one embodiment, each frame of audiodata for the first audio channel has an associated sequence number whichmay also be referred to as a frame index; wherein each frame of audiodata for the second audio channel has an associated sequence number suchthat each frame of audio data for the first audio channel has a sequencenumber equal to the respective sequence number of the correspondingframe of audio data for the second audio channel. For example, frame K(K being a positive integer) for the first audio channel corresponds toframe K for the second audio channel while frame K+1 for the first audiochannel corresponds to frame K+1 for the second audio channel.

The provision of respective buffers at the first and second audiorendering devices further allows synchronisation at a frame level, i.e.so as to ensure that frames for the first audio channel are rendered atthe same time as the corresponding frame for the second audio channel.To this end, in some embodiments, the first audio rendering device isconfigured to receive a message from the second audio rendering deviceindicative of a sequence number of a frame scheduled for release fromthe second frame buffer at the next buffer release time. Accordingly,the first audio rendering device may be configured to maintain the firstbuffer responsive to the received message. In particular, maintainingthe first buffer responsive to the received message may comprise one ormore of:

-   selecting a buffer depth of the first buffer;-   discarding a frame of audio data from the first buffer;-   delaying release of a frame of audio data from the first buffer;-   resetting the first buffer, e.g. so as to restart synchronisation.

The buffer depth of a buffer may be expressed as a number of frames thebuffer currently accommodates. It will be appreciated that a smallerbuffer depth reduces the overall latency of the system as well as memoryrequirements, while a larger buffer depth allows for an increasedcapability of the device to compensate for failed or delayed packettransmissions. Providing a mechanism to dynamically adapt the bufferdepth based on information about the current state of the buffer of theother audio rendering device allows for an improved optimisation of thebuffer depth. Typical buffer depths between 5 and 6 frames have beenfound to be suitable while a maximum buffer depth of 8 frames has beenfound sufficient for many situations. In some embodiments, the firstaudio rendering device may be configured to adapt the buffer depth, i.e.the number of frames currently accommodated in the buffer. For example,the first audio rendering device may be capable of change the bufferdepth up to a maximum buffer depth. The buffer depth may e.g. beexpressed as the current number of frames in the buffer or as an averagenumber of frames in the buffer, averaged over a predetermined timeinterval.

The exchange of information about which frame is scheduled to bereleased from the buffer also allows the audio rendering devices tohandle situations where a frame has not been received by one of thedevices or has been received too late to be included into the real-timeaudio rendering. In such situations, one of the audio rendering devicesmay discard one or more frames, so as to realign its rendering with thesequence of frames rendered by the other audio rendering device.Alternatively one of the devices may delay release of a frame so as towait for the other audio rendering device to get realigned. Whendelaying release of a frame the audio rendering device may insert aconcealment frame, e.g. a silent frame or a frame whose audio samplesare interpolated between the previous and the next, delayed frame.

It will be appreciated that, alternatively or additionally, the firstand second audio rendering devices may exchange other information thatmay be used for maintaining the respective buffers and for synchronisingthe release of respective sequences of frames of audio frames.

For example, in some embodiments, the received message from the secondaudio rendering device is further indicative of an elapsed time since areceipt, by the second audio rendering device, of said frame scheduledfor release from the second frame buffer at the next buffer releasetime. Alternatively or additionally, the received message from thesecond audio rendering device is further indicative of a second bufferdepth of the second buffer. Again this information may be used by thefirst audio rendering device to adapt its buffer depth. As above, itwill be appreciated that the second audio rendering device may receivecorresponding information from the first audio rendering device.

In some embodiments, one or both audio rendering devices may beconfigured to send commands or requests to the corresponding other audiorendering device, e.g. so as to request one or more of the actionsmentioned above, i.e. changing of the buffer depth, discarding a frame,delaying a frame and/or other actions. In some embodiments, to ensurethe action is synchronous on both audio rendering devices, the actionmay be scheduled to occur at a specific frame index, e.g. predeterminedby the algorithm, alternatively specified as part of the command orrequest.

Generally, at the beginning of a communications session, the wirelesscommunications device may exchange one or more initial data packets witheach of the audio rendering devices for setting up the communicationslink, e.g. so as to negotiate certain communications parameters.

Each audio packet may include one or more header sections and a payloadsection. The payload section may include the frame of audio data, suchas encoded audio data. The audio packet may comprise a sequence numberassociated with the frame of audio data.

The wireless communications device may be an audio-enabledcommunications device such as a smartphone or mobile phone, anaudio-enabled tablet, a cordless phone, a TV-set, a portable microphonearray etc. In particular, the wireless communications device may be anaudio-enabled portable communications device.

The wireless communications device may comprise an antenna, atransceiver and a communications controller, such as a Bluetooth LEcontroller for implementing the communication of audio packets to theaudio rendering devices. The wireless communications device may furthercomprise a signal processing unit configured to receive and process anaudio signal so as to create frames of digital audio samples.Alternatively or additionally, the wireless communications device maycomprise data storage for storing digital audio files encoding frames ofdigital audio samples.

Similarly, in some embodiments, the first audio rendering devicecomprises a first transceiver and a first antenna. Also, the secondaudio rendering device comprises a second transceiver and a secondantenna. The first audio rendering device may comprise a firstcommunications controller configured control the wireless communicationand to perform the steps of the method disclosed herein. In particular,the communication controller may be configured to implement one or morelayers of a suitable communications protocol.

The first audio rendering device may further comprise a signalprocessing circuit configured to process the received audio data fromthe communication controller and to generate an audio signal reflectingthe received audio data.

The first audio rendering device may further comprise an outputtransducer operatively coupled to the digital processing circuit andoperable to generate sound responsive to the audio signal.

Each of the first and second audio rendering devices may comprise ahearing instrument or hearing aid, for example jointly forming awireless binaural hearing aid system. In other embodiments, one or bothof the first and second audio rendering devices comprises a batterypowered audio-enabled device such as an earphone, headset, smartphone,remote microphone array, remote signal processor etc. Generally, thefirst audio rendering device and/or the second audio rendering devicemay be a user-worn device, such as a device worn at, behind and/or in auser’s ear. In particular, the first and second audio rendering devicesmay be configured to be worn at, behind and/or in respective ones of auser’s ears.

In particular, in some embodiments, the audio rendering system comprisesfirst and second hearing instruments or aids. Each of the first andsecond hearing instruments or aids may receive and deliver a binaurallyprocessed hearing loss compensated audio signal to a user or patient viarespective loudspeakers or receivers as discussed in further detailbelow with reference to the appended drawings. Each of the first andsecond hearing instruments or aids may comprise a BTE, RIE, ITE, ITC,CIC, etc. type of hearing instrument. Typically, only a severely limitedamount of power is available from a power supply of a hearinginstrument. For example, power is typically supplied from a conventionalZnO₂ battery in a hearing aid. In the design of a hearing aid, the sizeand the power consumption are important considerations.

Each of the first and second hearing instruments may comprise an inputtransducer, such as one or several microphones, configured to output anaudio signal based on a signal applied to the input transducer andrepresenting sound. Each of the first and second hearing instruments maycomprise a hearing loss processor configured to compensate a hearingloss of a user of the hearing aid and output a hearing loss compensatedaudio signal. The hearing loss compensated audio signal may be adaptedto restore loudness such that loudness of the applied signal as it wouldhave been perceived by a normal listener substantially matches theloudness of the hearing loss compensated signal as perceived by theuser. Each of the first and second hearing instruments or hearing aidsmay additionally comprise an output transducer, such as a receiver orloudspeaker, an implanted transducer, etc., configured to output anauditory output signal based on the hearing loss compensated audiosignal that can be received by the human auditory system, whereby theuser hears the sound. The input transducer may also comprise a telecoilthat converts a time-varying magnetic field at the telecoil into acorresponding varying analogue audio signal in which the instantaneousvoltage of the audio signal varies continuously with the varyingmagnetic field strength at the telecoil. Telecoils may be used toincrease the signal to noise ratio of speech from a speaker addressing anumber of people in a public place, e.g. in a church, an auditorium, atheatre, a cinema, etc., or through a public address systems, such as ina railway station, an airport, a shopping mall, etc. Speech from thespeaker is converted to a magnetic field with an induction loop system(also called “hearing loop”), and the telecoil is used to magneticallypick up the magnetically transmitted speech signal. The input transducermay further comprise at least two spaced apart microphones, and abeamformer configured for combining microphone output signals of the atleast two spaced apart microphones into a directional microphone signal.The input transducer may comprise one or more microphones and a telecoiland a switch, e.g. for selection of an omnidirectional microphonesignal, or a directional microphone signal, or a telecoil signal, eitheralone or in any combination, as the audio signal. Typically, theanalogue audio signal is made suitable for digital signal processing byconversion into a corresponding digital audio signal in ananalogue-to-digital converter whereby the amplitude of the analogueaudio signal is represented by a binary number. In this way, adiscrete-time and discrete-amplitude digital audio signal in the form ofa sequence of digital values represents the continuous-time andcontinuous-amplitude analogue audio signal. Throughout the presentdisclosure, the “audio signal” may be used to identify any analogue ordigital signal forming part of the signal path from the output of theinput transducer to an input of the hearing loss processor. Throughoutthe present disclosure, the “hearing loss compensated audio signal” maybe used to identify any analogue or digital signal forming part of thesignal path from the output of the hearing loss processor to an input ofthe output transducer possibly via a digital-to-analogue converter.

Each of the first and second radio transceivers may comprise both awireless transmitter and a wireless receiver. The transmitter andreceiver may share common circuitry and/or a single housing.Alternatively, the transmitter and receiver may share no circuitry, andthe wireless communication unit may comprise separate devices with thetransmitter and the receiver, respectively. Signal processing in each ofthe first and second audio rendering device may be performed bydedicated hardware or may be performed in one or more signal processors,or performed in a combination of dedicated hardware and one or moresignal processors. Likewise, the operations performed by each of thefirst and second communication controllers may be performed by dedicatedhardware or may be performed in one or more processors, or performed ina combination of dedicated hardware and one or more processors. As usedherein, the terms “processor”, “signal processor”, “controller”,“system”, etc., are intended to refer to microprocessor or CPU-relatedentities, either hardware, a combination of hardware and software,software, or software in execution. For example, a “processor”, “signalprocessor”, “controller”, “system”, etc., may be, but is not limited tobeing, a process running on a processor, a processor, an object, anexecutable file, a thread of execution, and/or a program. By way ofillustration, the terms “processor”, “signal processor”, “controller”,“system”, etc., designate both an application running on a processor anda hardware processor. One or more “processors”, “signal processors”,“controllers”, “systems” and the like, or any combination hereof, mayreside within a process and/or thread of execution, and one or more“processors”, “signal processors”, “controllers”, “systems”, etc., orany combination hereof, may be localized on one hardware processor,possibly in combination with other hardware circuitry, and/ordistributed between two or more hardware processors, possibly incombination with other hardware circuitry. Also, a processor (or similarterms) may be any component or any combination of components that iscapable of performing signal processing. For examples, the signalprocessor may be an ASIC processor, a FPGA processor, a general purposeprocessor, a microprocessor, a circuit component, or an integratedcircuit.

The present disclosure relates to different aspects including the systemdescribed above and in the following, corresponding apparatus, systems,methods, and/or products, each yielding one or more of the benefits andadvantages described in connection with one or more of the otheraspects, and each having one or more embodiments corresponding to theembodiments described in connection with one or more of the otheraspects and/or disclosed in the appended claims.

In particular, according to one aspect, disclosed herein is an audiorendering device; comprising:

-   at least one wireless communications interface configured to    -   receive a first plurality of audio packets from a wireless        communications device, the first plurality of audio packets        including frames of audio data for a first audio channel from a        set of one or more audio channels;    -   exchange messages with another audio rendering device, the other        audio rendering device being configured to receive a second        plurality of audio packets from said wireless communications        device, the second plurality of audio packets including frames        of audio data for a second audio channel from said set of one or        more audio channels;-   a signal processor configured to process the frames of audio data    included in the first plurality of audio packets for rendering by    the first audio rendering device;-   wherein the at least one wireless communications interface is    further configured to:    -   maintain a first buffer of received frames of audio data and to        release, at respective first buffer release times, frames of        audio data from said first buffer to the signal processor for        rendering;    -   receive one or more messages from the other audio rendering        device; and to    -   synchronise, based on the received one or more messages; the        first buffer release times with second buffer release times at        which the other audio rendering device releases frames of audio        data from a second buffer of received frames of audio data        maintained by the other audio rendering device.

The wireless communications interface may comprise a single antennaand/or a single transceiver and/or a single communications controllerfor implementing the receipt of audio packets from the wirelesscommunications device and the receipt of messages from the other audiorendering device. Alternatively, the audio rendering device may includeseparate antenna and/or separate transceivers and/or separatecommunications controllers for implementing the receipt of audio packetsfrom the wireless communications device and the receipt of messages fromthe other audio rendering device, respectively.

According to yet another aspect, disclosed herein is a method,implemented by a pair of audio rendering devices, the pair comprising afirst audio rendering device and a second audio rendering device, ofsynchronising audio content rendered by said pair of audio renderingdevices; the method comprising:

-   receiving, by the first audio rendering device from a wireless    communications device; a first plurality of audio packets, the first    plurality of audio packets including frames of audio data for a    first audio channel from a set of one or more audio channels;-   receiving, by the second audio rendering device from the wireless    communications device; a second plurality of audio packets, the    second plurality of audio packets including frames of audio data for    a second audio channel from said set of one or more audio channels;-   maintaining, by the first audio rendering device, a first buffer of    received frames of audio data and releasing frames of audio data    from said first buffer for rendering at respective first buffer    release times;-   maintaining, by the second audio rendering device, a second buffer    of received frames of audio data and releasing frames of audio data    from said second buffer for rendering at respective second buffer    release times;-   receiving, by the first audio rendering device, one or more messages    from the second audio rendering device; and-   synchronizing, by at least the first audio rendering device, the    first buffer release times with the second buffer release times    based on the received one or more messages.

According to yet another aspect, disclosed herein is an audio renderingdevice; comprising:

-   a first communications interface configured to receive a first    plurality of audio packets from a wireless communications device,    the first plurality of audio packets including audio data for a    first audio channel from a set of one or more audio channels;-   a second communications interface configured to wirelessly    communicate with another audio rendering device, the other audio    rendering device being configured to receive a second plurality of    audio packets from said wireless communications device, the second    plurality of audio packets including audio data for a second audio    channel from said set of one or more audio channels; for each audio    packet in the first plurality of audio packets, the second plurality    of audio packets comprising a corresponding audio packet, such that    audio data in the audio packet in the first plurality of audio    packets and audio data in the corresponding audio packet from the    second plurality of audio packets are configured for simultaneous    rendering as part of, respectively, the first audio channel and the    second audio channel; wherein the first plurality of audio packets    and the second plurality of audio packets are transmitted by the    wireless communications device according to a transmission schedule    such that audio packets from the first plurality of audio packets    are scheduled for transmission to the audio rendering device and    that each audio packet of the second plurality of audio packets is    scheduled for transmission at a delay interval after the    corresponding audio packet from the first plurality of audio packets    is scheduled for transmission;-   a signal processor configured to render audio content based on the    audio data included in the first plurality of audio packets;

wherein the audio rendering device is configured to determine, based oncommunication with the other audio rendering device, the delay intervaland to delay rendering of each of the first plurality of audio packetsby the determined delay interval.

An audio rendering device includes: at least one wireless communicationsinterface configured to receive a first plurality of audio packets froma wireless communication device, the first plurality of audio packetsincluding frames of audio data for a first audio channel from a set ofone or more audio channels; and a processing unit; wherein the audiorendering device is configured to release, at respective first bufferrelease times, the frames of the audio data for the first audio channelfrom a first buffer for rendering by the processing unit; wherein theaudio rendering device is configured to receive one or more messagesfrom an other audio rendering device; and wherein the audio renderingdevice is configured to synchronize the first buffer release times withsecond buffer release times associated with the other audio renderingdevice based on the received one or more messages.

Optionally, the first buffer release times are regularly spaced apart bya first interval, and wherein the second buffer release times areregularly spaced apart by a second interval equal to the first interval.

Optionally, the audio rendering device is configured to determine firstpacket receipt times indicative of respective times of receipt of audiopackets of the first plurality of audio packets from the wirelesscommunication device, and to determine the first buffer release timesbased on the determined first packet receipt times

Optionally, the audio rendering device is configured to determine atleast one of the first buffer release times based on a delay intervalbetween a transmission of one of the first plurality of audio packetsand a transmission of one of a second plurality of audio packets for theother audio rendering device.

Optionally, the audio rendering device is configured to release one ofthe frames of the audio data from the first buffer at a time that isequal to a packet receipt time for the one of the frames of the audiodata in the first plurality of audio packets delayed by a buffer delayconfigured to compensate for the delay interval.

Optionally, at least one of the one or more messages is indicative of atime of receipt, by the other audio rendering device, of a previous oneof a second plurality of audio packets; and wherein the audio renderingdevice is configured to determine a delay interval based on (1) the atleast one of the one or more messages, and (2) a time of receipt of aprevious one of the first plurality of audio packets by the audiorendering device.

Optionally, at least one of the one or more messages from the otheraudio rendering device is indicative of a sequence number of a framescheduled for release at the other audio rendering device.

Optionally, the audio rendering device is configured to maintain thefirst buffer responsive to the received one or more messages.

Optionally, at least one of the one or more messages from the otheraudio rendering device is indicative of an elapsed time since a receipt,by the other audio rendering device, of a frame of audio data scheduledfor release from the a second buffer associated with the other audiorendering device at a next buffer release time.

Optionally, at least one of the one or more messages from the otheraudio rendering device is indicative of a buffer depth of a secondbuffer associated with the other audio rendering device.

An audio rendering system includes the audio rendering device and thewireless communication device.

Optionally, the wireless communication device is configured to transmitthe first plurality of audio packets to the audio rendering device, andto transmit a second plurality of audio packets to the other audiorendering device according to a transmission schedule.

Optionally, the wireless communication device is configured to transmiteach audio packet of the second plurality of audio packets to the otheraudio rendering device at a delay interval after a corresponding audiopacket of the first plurality of audio packets is transmitted.

Optionally, the audio rendering device is configured to determine thedelay interval based on at least one of the one or more messages.

An audio rendering system includes the audio rendering device, and theother audio rendering device.

Optionally, the other audio rendering device is configured to receive asecond plurality of audio packets, the second plurality of audio packetsincluding frames of audio data for a second audio channel from the setof one or more audio channels.

Optionally, the second audio rendering device is configured to release,at the respective second buffer release times, the frames of audio datafor the second audio channel from a second buffer for rendering.

Optionally, the audio rendering device and the other audio renderingdevice are configured to simultaneous render one of the frames of theaudio data in the first plurality of audio packets for the first audiochannel, and one of the frames of the audio data in the second pluralityof audio packets for the second audio channel.

Optionally, each frame of audio data in the first plurality of audiopackets for the first audio channel has an associated sequence number,and wherein each frame of audio data in the second plurality of audiopackets for the second audio channel has an associated sequence number.

Optionally, the audio rendering device is configured to maintain thefirst buffer by: selecting a buffer depth of the first buffer;discarding a frame of audio data from the first buffer; delaying releaseof a frame of audio data from the first buffer; resetting the firstbuffer; or one or more of the foregoing.

Optionally, each frame of audio data for the first audio channel has asequence number equal to a corresponding sequence number of acorresponding frame of audio data for the second audio channel.

Optionally, each frame of audio data in the first plurality of audiopackets has a sequence number equal to a corresponding sequence numberof a corresponding one of the frames of audio data in the secondplurality of audio packets.

An audio rendering device includes: at least one wireless communicationinterface configured to receive a first plurality of audio packets froma wireless communication device, the first plurality of audio packetsincluding frames of audio data for a first audio channel from a set ofone or more audio channels, wherein the at least one wirelesscommunication interface is also configured to receive one or moremessages from an other audio rendering device, the other audio renderingdevice being configured to receive a second plurality of audio packetsfrom the wireless communication device, the second plurality of audiopackets including frames of audio data for a second audio channel fromthe set of one or more audio channels; a signal processor configured toprocess the frames of audio data included in the first plurality ofaudio packets for rendering; wherein the audio rendering device isconfigured to release, at respective first buffer release times, theframes of the audio data in the first plurality of audio packets from afirst buffer to the signal processor for rendering; and wherein theaudio rendering device is configured to synchronize, based on thereceived one or more messages, the first buffer release times withsecond buffer release times at which the other audio rendering devicereleases frames of audio data in the second plurality of audio packetsfrom a second buffer associated with the other audio rendering device.

A method of synchronizing audio content rendered by a pair of audiorendering devices, the pair of audio rendering devices comprising afirst audio rendering device and a second audio rendering device,includes: receiving, by the first audio rendering device, a firstplurality of audio packets from a wireless communication device, thefirst plurality of audio packets including frames of audio data for afirst audio channel from a set of one or more audio channels; receiving,by the second audio rendering device, a second plurality of audiopackets from the wireless communication device, the second plurality ofaudio packets including frames of audio data for a second audio channelfrom the set of one or more audio channels; releasing frames of audiodata in the first plurality of audio packets from a first buffer forrendering at respective first buffer release times; releasing frames ofaudio data in the second plurality of audio packets from a second bufferfor rendering at respective second buffer release times; receiving, bythe first audio rendering device, one or more messages from the secondaudio rendering device; and synchronizing, by at least the first audiorendering device, the first buffer release times with the second bufferrelease times based on the received one or more messages.

Other features and advantageous will be described below in the detaileddescription.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, preferred embodiments of the various aspects disclosedherein are described in more detail with reference to the appendeddrawings, wherein:

FIG. 1 schematically illustrates an embodiment of an audio renderingsystem.

FIG. 2 schematically illustrates another embodiment of an audiorendering system.

FIG. 3 schematically illustrates timing aspects of the communicationbetween the devices of an embodiment of an audio rendering system.

FIG. 4 shows a schematic flow diagram of a process performed by one ofthe audio rendering device of an audio rendering system as describedherein.

FIG. 5 schematically illustrates an example of an audio packet.

FIG. 6 illustrates and example of the operation of the transmission offrames of audio data by the wireless communications device of an audiorendering system as described herein.

DETAILED DESCRIPTION OF EMBODIMENTS

Various embodiments are described hereinafter with reference to thefigures. Like reference numerals refer to like elements throughout. Likeelements will, thus, not be described in detail with respect to thedescription of each figure. It should also be noted that the figures areonly intended to facilitate the description of the embodiments. They arenot intended as an exhaustive description of the claimed invention or asa limitation on the scope of the claimed invention. In addition, anillustrated embodiment needs not have all the aspects or advantagesshown. An aspect or an advantage described in conjunction with aparticular embodiment is not necessarily limited to that embodiment andcan be practiced in any other embodiments even if not so illustrated, orif not so explicitly described.

In the following, preferred embodiments of the various aspects disclosedherein are described in more detail with reference to the appendeddrawings and in the context of hearing instruments. In the followingembodiments, one or each of the first and second audio rendering devicescomprises a respective hearing instrument as discussed in additionaldetail below. The skilled person will understand that the accompanyingdrawings are schematic and simplified for clarity.

FIG. 1 schematically illustrates an embodiment of an audio renderingsystem. In particular, the audio rendering system comprises a wirelesscommunications device 50, a first audio rendering device 10L and asecond audio rendering device 10R. The wireless communications device 50is communicatively coupled to the first audio rendering device 10L via afirst wireless communications link 12L and to the second audio renderingdevice 10R via a second wireless communications link 12R. Hence, thewireless communications device establishes respective, bi-directionalcommunications connections with each of the audio rendering devices. Thefirst wireless communications link 12L is a direct, bi-directional linkbetween the wireless communications device 50 and the first audiorendering device 10L; in particular, the communication between thewireless communications device 50 and the first audio rendering device10L does not involve the second audio rendering device 10R. Similarly,the second wireless communications link 12R is a direct, bi-directionallink between the wireless communications device 50 and the second audiorendering device 10R; in particular, the communication between thewireless communications device 50 and the second audio rendering device10R does not involve the first audio rendering device 10L. Moreover, thefirst audio rendering device 10L is communicatively coupled to thesecond audio rendering device 10R via a direct wireless communicationslink 13. In particular, the communications link 13 between the firstaudio rendering device 10L and the second audio rendering device 10Rdoes not involve the wireless communications device 50.The wirelesscommunications device 50 may be a smartphone or mobile phone, anaudio-enabled tablet, a cordless phone, a TV-set, a portable microphonearray etc. The first and second audio rendering devices may berespective hearing instruments or aids as will be described in greaterdetail below.

FIG. 2 schematically illustrates an embodiment of an audio renderingsystem. As in the previous embodiment, the audio rendering systemcomprises a wireless communications device 50, a first audio renderingdevice and a second audio rendering device. The first and second audiorendering devices form a wireless binaural hearing aid system comprisinga left ear hearing aid or instrument 10L and a right ear hearing aid orinstrument 10R, each of which comprises a wireless communication unitfor connection to the wireless communications device 50 and to therespective other hearing instrument. In the present embodiment, the leftear and right ear hearing aids 10L, 10R are connected to each other viaa bi-directional wireless communication channel or link 13. A unique IDmay be associated with each of the left ear and right ear hearing aids10L, 10R. Alternatively, the left and right ear hearing aids may beconnected with each other via another wireless or wired communicationschannel, e.g. via a magnetic inductive link.

Each hearing aid is further communicatively connected to the wirelesscommunications device 50 via wireless communication links 12L and 12R,respectively. Hence, the wireless communications device 50 establishesrespective bidirectional communications connections with each of thehearing aids.

Wireless communication between the respective devices of the illustratedbinaural hearing aid system may be performed via the 2.4 GHz industrialscientific medical (ISM) band which may comprise a number of spacedapart frequency bands or channels. Each of the spaced apart frequencybands or channels may possess a bandwidth between 0.5 - 2.0 MHz such asabout 1.0 MHz. The hearing aids 10L, 10R are configured to communicatewith the wireless communications device 50 in accordance with BluetoothLow Energy (Bluetooth LE) for example according to the Bluetooth CoreSpecification Version 4.1, 4.2 or 5. However, communications controllersof the wireless communication units of each of the left and right earhearing aids 10L, 10R have been adapted so as to enable receipt ofreal-time audio data sets through each of the wireless communicationlinks 12L, 12R as explained in further detail below and for synchronisedrendering of the received audio data. To this end, the communicationscontrollers of the hearing aids 10L, 10R have further been adapted toenable communication between the hearing aids via wirelesscommunications link 13. The communication via communications link 13 isalso performed in the 2.4 GHz ISM band but may employ a communicationsprotocol other than Bluetooth.

The left hearing aid 10L and the right hearing aid 10R may besubstantially identical in some embodiments expect for theabove-described unique ID. Accordingly, the following description of thefeatures of the left hearing aid 10L also applies to the right hearingaid 10R. The left hearing aid 10L may comprise a ZnO₂ battery (notshown) that is connected for supplying power to the hearing aid circuit14. The left hearing aid 10L comprises an input transducer in the formof a microphone 16. The microphone 16 outputs an analogue or digitalaudio signal based on an acoustic sound signal arriving at themicrophone 16 when the left hearing aid 10L is operating. If themicrophone 16 outputs an analogue audio signal the hearing aid circuit14 may comprise an analogue-to-digital converter (not shown) whichconverts the analogue audio signal into a corresponding digital audiosignal for digital signal processing in the hearing aid circuit 14. Inparticular in a hearing loss processor 24L that is configured tocompensate a hearing loss of a user of the left hearing aid 10.Preferably, the hearing loss processor 24L comprises a dynamic rangecompressor well-known in the art for compensation of frequency dependentloss of dynamic range of the user often termed recruitment in the art.Accordingly, the hearing loss processor 24L outputs a hearing losscompensated audio signal to a loudspeaker or receiver 32L. Theloudspeaker or receiver 32 converts the hearing loss compensated audiosignal into a corresponding acoustic signal for transmission towards aneardrum of the user. Consequently, the user hears the sound arriving atthe microphone; however, compensated for the user’s individual hearingloss. The hearing aid may be configured to restore loudness, such thatloudness of the hearing loss compensated signal as perceived by the userwearing the hearing aid 10 substantially matches the loudness of theacoustic sound signal arriving at the microphone 16 as it would havebeen perceived by a listener with normal hearing.

The hearing aid circuit 14L further includes a wireless communicationsunit which comprises a radio portion or transceiver 34L that isconfigured to communicate wirelessly with the right or second hearingaid 10R and with the wireless communications device 50. The wirelesscommunications unit comprises a first communications controller 26Lperforming various tasks associated with the communications protocolsand possibly other tasks. The hearing loss processor 24L may comprise asoftware programmable microprocessor such as a Digital Signal Processor.The operation of the left hearing aid 10L may be controlled by asuitable operating system executed on the software programmablemicroprocessor. The operating system may be configured to manage hearingaid hardware and software resources, e.g. including the hearing lossprocessor 24L and possibly other processors and associated signalprocessing algorithms, the wireless communications unit, certain memoryresources etc. The operating system may schedule tasks for efficient useof the hearing aid resources and may further include accounting softwarefor cost allocation, including power consumption, processor time, memorylocations, wireless transmissions, and other resources. The operatingsystem controls, in cooperation with the first communications controller26L, the radio transceiver 34L to perform the bi-directional wirelesscommunication with the right or second hearing aid 10R and with thewireless communications device 50 in accordance with the presentmethodology or protocol for receiving and synchronising audio data. Thewireless communications device 50 may operate as a master device and theleft and right hearing aids 10L, 10R as respective slaves in connectionwith bi-directional data communication between the device under theaudio-enabled Bluetooth LE protocol.

The wireless communications device 50 comprises a radio portion orcircuit 54 that is configured to communicate wirelessly with thecorresponding radio portions or circuits 34L, 34R of the left and righthearing aids 10L, 10R, respectively. The wireless communications device50 also comprises a wireless communication unit which comprises aBluetooth LE controller 56 performing the various communication protocolrelated tasks in accordance with the audio-enabled Bluetooth LE protocoland possibly other tasks. Audio or other data packets or data sets fortransmission over the wireless communication links 12L, 12R are suppliedby the Bluetooth LE controller 56 to the radio circuit 54. Data packetsreceived by the radio portion or circuit 54 via RF antenna 53 areforwarded to the Bluetooth LE controller 56 for further data processing.The skilled person will appreciate that the wireless communicationsdevice 50 typically will include numerous additional hardware andsoftware resources in addition to those schematically illustrated as iswell-known in the art of mobile phones.

The audio packets generated and transmitted by the wirelesscommunications device 50 comprise respective frames of audio data suchthat each hearing aid may receive the audio data and deliver audiosignal to the user or patient via the respective loudspeakers orreceivers 32L, 32R. Optionally, the hearing aids may process thereceived audio data so as to compensate for hearing loss, e.g. so as toprovide a binaurally processed hearing loss compensated audio signal.The hearing aids 10L,R are further configured to exchange data packetsincluding messages or other control data with each other, using therespective radio transceivers 34L, 34R and antenna 44L, 44R. Theexchanged messages may include control information or data for exampleto synchronize operation between the left and right hearing aids 10L,10R as will be described in more detail below.

The transmission of audio packets by the wireless communications device50 will typically correspond to environmental conditions with low levelsof interfering electromagnetic noise in the utilized frequency band orbands such that transmission of each audio packet may be successful atthe first transmission attempt or first transmission. In the lattersituation there is no need for retransmission of the audio packets.However, the wireless communications device 50 may be configured to copewith a certain error rate in the transmitted audio packets. This featureis particularly helpful for audio packet transmission in wirelessbinaural hearing instrument systems where the shadowing effect of theuser’s head may lead to a relatively high packet error rate (PER). Thedata packet transmission methodology may enable retransmission of lostaudio packets. The number of retransmission of an audio packet may beperformed until an acknowledgement of successful receipt has beenreceived by the wireless communications device from the correspondinghearing aid. It will be appreciated that, in some embodiments, thenumber of retransmissions may be limited to a certain maximum number oftimes. In some embodiments, when an audio packet has been retransmitteda large number of times, the resulting delay may be compensated by thewireless communications device by skipping one or more subsequent audioframes and/or by temporarily transmitting a larger number of frames,e.g. as illustrated in FIG. 6 . Generally, audio packet transmissionlatency is an important feature of the transmission methodology orprotocol if the respective audio data or frames of the audio packetsrepresent real time audio signals of the left and/or right hearing aids10L, 10R. The loss of audio frames from time to time when a particularaudio packet has been unsuccessfully retransmitted the maximum number oftimes or an increased transmission latency due to multipleretransmissions may be compensated or at least mitigated by the hearingaids. Loss of audio packets may be mitigated by adding a suitable audiocodec to the hearing aid circuit 14L, 14R. The audio codec may be ableto handle a certain amount of audio frame loss of an incoming real timeaudio data stream from the first or second communication controller 26L,26R. The audio codec may for example be configured to execute a PacketLoss Concealment algorithm to perceptually mask the lost audio frames ofincoming real time audio data stream.

Moreover, the communications controllers 26L and 26R comprise respectiveframe buffers 261L and 261R, respectively. Alternatively, the buffersmay be implemented in the respective transceiver circuits 34L, 34R. Eachframe buffer is configured to temporarily buffer one or more receivedframes of audio data so as to allow the communications controller toforward audio frames at a constant rate to the corresponding hearingloss processor 24L, 24R, respectively, for signal processing of thereceived audio frames, as will be described in more detail below.

FIG. 3 illustrates operation of an embodiment of an audio renderingsystem, e.g. one of the systems described in connection with FIG. 1 orFIG. 2 .

In particular, the wireless communications device 50 transmits audiopackets according to a transmission schedule such that the audio packetsare transmitted at regularly spaced apart transmission events. PacketsP1L, P2L etc. of a first plurality of audio packets are transmitted tothe left hearing aid while audio packets P1R, P2R etc. of a secondplurality of audio packets are transmitted to the right hearing aid. Thetransmission times of packets P1L, P2L is spaced apart by the sameinterval as the transmission times of packets P1R and P2R. However,transmission of packet P1R is delayed relative to the transmission ofcorresponding packet P1L by a delay interval Δ. Typically, the delayinterval Δ is constant for a given communications session, i.e. constantfor all audio packets of an audio stream.

The left hearing aid 10L receives the packets P1L, P2L etc. at regularintervals, while the right hearing aid 10R receives the packets P1R, P2Retc. at regular intervals of the same interval length. However due tothe delayed transmission, the right hearing aid receives each packetlater than the left hearing aid receives the corresponding packet. Itwill be appreciated that this delay may further be influenced by otherlatency factors. Moreover, it will be appreciated that, in somesituations, the packets to the left hearing aid will be delayed relativeto the corresponding packets of the right hearing aid instead.

Each of audio packets includes a frame of audio data, and the frameshave an associated sequence number, also referred to as frame index.During normal transmission audio packet P1L includes frame number 1 ofthe left audio channel while P1R includes frame number 1 of the rightaudio channel, etc.

Upon receipt of an audio packet, each hearing aid places thecorresponding frame of audio data into its frame buffer as the mostrecent frame. The hearing aid further releases the oldest frame from theframe buffer for processing by the signal processing circuit of thehearing loss circuit and for subsequent rendering by the receiver. Thebuffer is configured to hold a limited number of frames where the numberof frames is referred to as the buffer depths. Typical buffer depthsvary between 3 and 8 frames, such as 5-6 frames.

As the release from the frame buffer of each hearing aid is triggered bythe time of receipt of a new audio packet, synchronized rendering of theaudio frames by both hearing aids requires one of the hearing aids (inthe example of FIG. 3 the left hearing aid) to delay release of eachaudio frame from the buffer by an additional delay so as to compensatefor the delay Δ inherent in the transmission schedule of the wirelesscommunications device and possible other latency factors.

To this end, the left and right hearing aids exchange messages 33 and 34so as to exchange control data for synchronizing the rendering of thereceived audio data. The messages 33 and 34 are exchanged as lowerpriority data packets, e.g. such that at each communication event only asingle message is transmitted either from the right hearing aid to theleft hearing aid (illustrated by arrow 33) or from the left hearing aidto the right hearing aid (illustrated by arrow 34). Moreover, thecontrol messages 33, 34 may be exchanged at a rate smaller than thetransmission rate of the audio packets. It will be appreciated thatother embodiments of an audio rendering system may use othertransmission protocols for the exchanged messages. For example, otherembodiments may exchange messages in both directions at eachtransmission event.

The exchanged messages include control data for use by the respectivehearing aids for the synchronization of the rendering of the audio data.

In particular the exchanged messages include information from which thehearing aids determine the delay Δ. In a particular embodiment, thehearing aid 10R transmitting a control message 33 includes informationabout the time T2 elapsed since the receipt of the most recent audiopacket P1R by said hearing aid 10R. The hearing aid 10L receiving thecontrol message 33 may thus determine the time T1 elapsed since itreceived its most recent audio packet P1L and determine the applicabledelay Δ from these times, e.g. as Δ = T1 - T2. The other hearing aid mayalso determine the applicable delay from a corresponding reverse controlmessage 34 including corresponding information. Even though controlmessages are exchanged repeatedly, it will be appreciated that, in someembodiments, only the control messages exchanged toward the beginning ofan audio transmission include the above timing information for thedetermination of the delay Δ. As the transmission delay by the wirelesscommunications device remains stable, the determined value for the delaymay be utilized throughout the transmission. Nevertheless, in otherembodiments, the above timing information is exchanged repeatedly, e.g.so as to allow the hearing aids to adjust the delay, e.g. so as tomitigate possible changes in the transmission environment and possiblechanges in the transmission latencies of the respective transmissionchannels. While, in the example of FIG. 3 , the audio packets to theright hearing aid are delayed relative to the corresponding audiopackets to the left hearing aids, it will be appreciated that therelative shift may be reverse, i.e. such that the audio packets to theleft hearing aid are delayed relative to the corresponding audio packetsto the right hearing aid. Hence, in such a situation, the left hearingaid may have to delay its buffer release times while the right hearingaid may not add any delay to the buffer release time to accommodate forthe transmission delay.

In addition to the above timing information, some or all of theexchanged control messages also include information about the status ofthe frame buffer of the hearing aid that is transmitting the respectivecontrol message.

In particular, a hearing aid may transmit information to the otherhearing aid about the sequence number of the oldest frame in the framebuffer, i.e. of the frame that is scheduled to be released from thebuffer at the next buffer release event. Moreover, the hearing aid maytransmit information about how long the oldest frame has been waiting inthe buffer and/or other information, such as the buffer depth, etc.

The receiving hearing aid may use this information in a variety of waysto ensure synchronized release of frames from the frame buffer. Forexample, the hearing aid receiving a control message from the otherhearing aid indicating the sequence number of the oldest frame in theframe buffer of the other hearing aid may compare this number with thesequence number of the oldest frame in its own frame buffer. Normallythe sequence numbers are equal; however; packet losses, discarded audiopackets, delays etc. may cause the sequence numbers of the oldest framesin the respective buffers to be different from each other. In such asituation, the hearing aid having an oldest frame in the frame bufferthat has a lower sequence number than the oldest frame in the otherhearing aid’s frame buffer, may skip the oldest frame and release thesubsequent frame from the buffer instead, so as to reestablishsynchronization.

Alternatively, the hearing aid having a frame of higher sequence numberas oldest frame in the buffer may delay release of the oldest frame andinstead create a concealment frame.

In some embodiments, a hearing aid may dynamically change the bufferdepth of its frame buffer, e.g. responsive to changes in thetransmission environment.

For example, if a hearing aid receives information from the otherhearing aid that the other hearing aid has a higher buffer depth andalso a lower frame index it may be operable to increase its own bufferdepth by duplicating its first entry. If the opposite is true, i.e. thehearing aid has fewer frames in its buffer and also a higher frameindex, this hearing aid may be operable to decrease its own buffer depthby removing an entry, e.g. the first entry.

In some embodiments a hearing aid may monitor the quality of thecommunications link to the wireless communications device, e.g. bymonitoring the gaps in the sequence of received frame indices. Forexample, if the hearing aid detects large gaps in relation to framesbeing skipped on the transmitting side, it may be operable toreconfigure the communications link to use more buffers on thetransmitting side. For example, in the example of FIG. 6 , an increasefrom 2 to 4 buffers would have prevented frames 6 and 7 from beingskipped.

Hence, based on the exchanged messages between the hearing aids and/orbased on the detected quality of the communications link to the wirelesscommunications device, the hearing aids may synchronize the processingof the received audio frames both in respect of the sequence numbers ofthe currently processed frames and in respect of the exact timing of theprocessing of frames. The synchronizing of sequence numbers seeks toensure that the frames of audio data processed by the hearing aidscorrespond to each other (i.e. have the same sequence number). Thesynchronizing of the timing of the processing of frames seeks to reduceor even eliminate any shift/delay in the processing of the receivedframes relative to the other hearing aid.

To this end, the exchanged messages may comprise one or more parameters,which may be combined as needed, e.g. in a static or dynamic way. Theexchanged parameters included in the messages may be one or more of thefollowing parameters and/or other parameters:

-   ConnectionOffset: The time offset from the current message’s    timestamp until the next connection event, e.g. the next BLE    connection event. This parameter may be used for sample    synchronization within a frame.-   MaxDepth: The maximum buffer depth, i.e. the maximum number of    frames which can be stored in the buffer.-   CurrentDepth: The current number of frames stored in the buffer.-   AverageDepth: The average number of frames stored in the buffer,    where the average is defined over a suitable, e.g. a predetermined,    period of time.-   NextAudFrameIdxAvailable (for rendering): The index of the ‘oldest’    audio frame in the buffer.-   NextAudFrameldxExpected (for rendering) : The next audio frame index    expected by the rendering system. Except when frames are being    inserted or removed, this value is normally incremented for each    audio frame interval.

FIG. 4 shows a schematic flow diagram of a process performed by one ofthe audio rendering device of an audio rendering system as describedherein, e.g. of a system as described in connection with FIG. 1 or FIG.2 .

In initial step S1, the audio rendering device sets up respectivecommunication links with the wireless communications device and theother audio rendering device. As part of this step, the audio renderingdevice may receive and/or transmit setup messages from/to the wirelesscommunications device and/or the other audio rendering device, as iswell known in the art. The audio rendering device further sets up itsinternal processing, e.g. including initializing the frame buffer.

Once the communications links are set up, the process proceeds at stepS2 where it receives an audio packet from the wireless communicationsdevice. The audio packet includes a frame of audio data.

In step S3, the audio rendering device places the received audio framein the frame buffer as newest frame.

In step S4, the audio rendering device releases the oldest frame in theframe buffer for processing by the digital signal processing circuit andrendering by a loudspeaker. The time at which the audio rendering devicereleases the frames may be determined by the time of receipt of a newframe and by a determined delay so as to compensate for a relativeshift/delay of transmission times of the packet transmissions to therespective audio rendering devices.

If the process has received a control message from the other audiorendering device, the process proceeds at step S5; otherwise the processproceeds at step S6. At step S5, the process processes the receivedcontrol messages so as to manage the buffer and/or determine theapplicable delay of buffer release times.

In step S6, the process determines whether a control message should betransmitted to the other audio rendering device. The transmission ofcontrol messages may e.g. be triggered by changes in the buffer statusor other operational trigger events or they may be sent at regularintervals. If a control message is to be sent, the process proceeds atstep S7; otherwise the process proceeds at step S8.

At step S7, the process creates and transmits a control message to theother audio rendering device of the system. As described above, thecontrol message may include one or more control parameters.

At step S8, the process determines whether the stream of audio data iscompleted. If so, the process proceeds to step S9 where it finishesprocessing the remaining frames in the buffer and terminates; otherwisethe process returns to step S2.

FIG. 5 schematically illustrates an example of an audio packet. Theaudio packet 60 includes a frame 62 of audio data and a sequence number61 (frame index) associated with the frame 62. It will be appreciatedthat the audio packet may include additional sections, such as a CRC,header information etc.

FIG. 6 illustrates and example of the operation of the transmission offrames of audio data by the wireless communications device of an audiorendering system as described herein, e.g. of a system as described inconnection with FIG. 1 or FIG. 2 .

Generally, the transmission of audio packets may be performed accordingto a Bluetooth protocol as described in the Bluetooth specification. Thedrawing illustrates frames of audio data 60 being generated periodicallyfor transmission to one of the audio rendering devices. The frames ofthe example of FIG. 6 are sequentially enumerated by frame indices 1-12.The generated frames are queued for transmission in one or moretransmission buffers 65. The wireless communications device transmitsthe queued frames from the buffer to the corresponding audio renderingdevice at respective connection events as described herein. Once thewireless communications device has received a transmit acknowledgment 68from the receiving device in respect of a transmitted frame, thewireless communications device removes the corresponding frame from thebuffer, thus making a buffer slot available again for accommodating asubsequent frame. The wireless communications device may allow up to amaximum number of buffered frames at any time. In the example of FIG. 6, it is assumed that the connection is configured to queue up to twoframes for transmission. The available buffer slots (or separatebuffers) at any time are indicated in FIG. 6 as respective buffer counts67 below the time lime 66. When a frame is queued for transmission thebuffer count is decreased; when successful transmission of a frame hasbeen acknowledged, the buffer count is increased. When all buffer slotsare occupied, i.e. when the buffer count of available buffer slots iszero, the generated frames are not queued, but skipped. In the exampleof FIG. 6 , this is illustrated by frames 6 and 7 being skipped due toframes 4 and 5 not yet having being acknowledged yet. In cases of delaysin the transmission of audio packets, the wireless communications devicemay temporarily transmit audio packets at shorter intervals so as tocatch up with the periodic generation of frames. In FIG. 6 , thiscatching up is illustrated for e.g. frames 2 and 3 which are transmitted(and acknowledged) at a shorter interval than the frame interval (thisalso applies to frames 4,5,8 and 9,10 in FIG. 6 ).

Although the above embodiments have mainly been described with referenceto certain specific examples, various modifications thereof will beapparent to those skilled in art without departing from the spirit andscope of the claimed invention. For example, while the various aspectsdisclosed herein have mainly been described in the context of hearingaids, they may also be applicable to other types of audio renderingdevices.

Similarly, while the various aspects disclosed herein have mainly beendescribed in the context of a short-range RF communication between theaudio rendering devices, it will be appreciated that the communicationsbetween the audio rendering devices may use other communicationtechnologies, such as other wireless or even wired technologies. In oneexample, the audio rendering devices, e.g. a pair of hearing aids, maycommunicate with each other via a magnetic inductive link.

At least some of the embodiments disclosed herein may be summarized asfollows:

Embodiment 1: An audio rendering system; comprising a wirelesscommunications device, a first audio rendering device and a second audiorendering device;

-   wherein the wireless communications device is configured to transmit    a first plurality of audio packets to the first audio rendering    device and to transmit a second plurality of audio packets to the    second audio rendering device, the first plurality of audio packets    including frames of audio data for a first audio channel from a set    of one or more audio channels and the second plurality of audio    packets including frames of audio data for a second audio channel    from said set of one or more audio channels;-   wherein the first audio rendering device is configured to maintain a    first buffer of received frames of audio data for the first audio    channel and to release, at respective first buffer release times,    frames of audio data for the first audio channel from said first    buffer for rendering;-   wherein the second audio rendering device is configured to maintain    a second buffer of received frames of audio data for the second    audio channel and to release, at respective second buffer release    times, frames of audio data for the second audio channel from said    second buffer for rendering;-   wherein the first audio rendering device is configured to receive    one or more messages from the second audio rendering device; and-   wherein at least the first audio rendering device is configured to    synchronise the first buffer release times with the second buffer    release times based on the received one or more messages.

Embodiment 2: An audio rendering system according to embodiment 1;wherein the first buffer release times are regularly spaced apart by afirst interval and wherein the second buffer release times are regularlyspaced apart by a second interval equal to the first interval.

Embodiment 3: An audio rendering system according to any one of thepreceding embodiments; wherein the wireless communications device isconfigured to transmit the first plurality of audio packets and thesecond plurality of audio packets according to a transmission schedulesuch that audio packets of the first plurality of audio packets arescheduled for transmission to the first audio rendering device and thateach audio packet of the second plurality of audio packets is scheduledfor transmission to the second audio rendering device at a delayinterval after a corresponding audio packet of the first plurality ofaudio packets is scheduled for transmission; and wherein at least thefirst audio rendering device is configured to determine the delayinterval based on at least one of the exchanged messages.

Embodiment 4: An audio rendering system according to embodiment 3;wherein the first audio rendering device is configured to

-   determine first packet receipt times indicative of respective times    of receipt of audio packets of the first plurality of audio packets    from the wireless communications device;-   determine the first buffer release times from the determined first    packet receipt times and from the delay interval.

Embodiment 5: An audio rendering system according to embodiment 4;wherein the first audio rendering device is configured to release audiopackets from the first buffer at the determined packet receipt timesdelayed by a buffer delay configured to compensate for one or moredelays, including for said delay interval.

Embodiment 6: An audio rendering system according to any one ofembodiments 3 through 5; wherein at least the first audio renderingdevice is configured to receive a message from the second audiorendering device indicative of a time of receipt, by the second audiorendering device, of a previous one of the second plurality of audiopackets; and to determine the delay interval from the received messageand from a time of receipt of a previous one of the first plurality ofaudio packets by the first audio rendering device.

Embodiment 7: An audio rendering system according to any one of thepreceding embodiments; wherein, for each frame of audio data for thesecond audio channel, the frames of audio data for the first audiochannel comprises a corresponding frame of audio data, such that theaudio data in the frame for the second audio channel and audio data inthe corresponding frame for the first audio channel are configured forsimultaneous rendering as part of, respectively, the first audio channeland the second audio channel.

Embodiment 8: An audio rendering system according to embodiment 7;wherein each frame of audio data for the first audio channel has anassociated sequence number; wherein each frame of audio data for thesecond audio channel has an associated sequence number, such that eachframe of audio data for the first audio channel has a sequence numberequal to the respective sequence number of the corresponding frame ofaudio data for the second audio channel.

Embodiment 9: An audio rendering system according to embodiment 8;wherein the first audio rendering device is configured to receive amessage from the second audio rendering device indicative of a sequencenumber of a frame scheduled for release from the second frame buffer atthe next buffer release time.

Embodiment 10: An audio rendering system according to embodiment 9;wherein the first audio rendering device is configured to maintain thefirst buffer responsive to the received message.

Embodiment 11: An audio rendering system according to embodiment 10;wherein maintaining the first buffer responsive to the received messagecomprises one or more of:

-   selecting a buffer depth of the first buffer;-   discarding a frame of audio data from the first buffer;-   delaying release of a frame of audio data from the first buffer;-   resetting the first buffer.

Embodiment 12: An audio rendering system according to any one ofembodiments 9 through 11; wherein the received message from the secondaudio rendering device is further indicative of an elapsed time since areceipt, by the second audio rendering device, of said frame scheduledfor release from the second frame buffer at the next buffer releasetime.

Embodiment 13: An audio rendering system according to any one ofembodiments 9 through 12; wherein the received message from the secondaudio rendering device is further indicative of a second buffer depth ofthe second buffer.

Embodiment 14: An audio rendering system according to any one of thepreceding embodiments; wherein the audio data is for stereo audio outputthat includes a plurality of stereo audio channels.

Embodiment 15: An audio rendering system according to any one of thepreceding embodiments; wherein the first and second audio renderingdevices are left and right hearing instruments, respectively.

Embodiment 16: An audio rendering system according to any one of thepreceding embodiments; wherein the wireless communications device isconfigured to transmit the first and second pluralities of audio packetsvia respective connection-oriented communications channels.

Embodiment 17: An audio rendering system according to any one of thepreceding embodiments; wherein the wireless communications device isconfigured to transmit the first and second pluralities of audio packetsvia respective BLE communications links.

Embodiment 18: An audio rendering system according to any one of thepreceding embodiments; wherein the first audio rendering devicecomprises a first transceiver and/or a first antenna configured toestablish wireless communication with the wireless communications deviceand with the second audio rendering device.

Embodiment 19: An audio rendering device; comprising:

-   at least one wireless communications interface configured to    -   receive a first plurality of audio packets from a wireless        communications device, the first plurality of audio packets        including frames of audio data for a first audio channel from a        set of one or more audio channels;    -   exchange messages with another audio rendering device, the other        audio rendering device being configured to receive a second        plurality of audio packets from said wireless communications        device, the second plurality of audio packets including frames        of audio data for a second audio channel from said set of one or        more audio channels;-   a signal processor configured to process the frames of audio data    included in the first plurality of audio packets for rendering by    the first audio rendering device;-   wherein the at least one wireless communications interface is    further configured to:    -   maintain a first buffer of received frames of audio data and to        release, at respective first buffer release times, frames of        audio data from said first buffer to the signal processor for        rendering;    -   receive one or more messages from the other audio rendering        device; and to    -   synchronise, based on the received one or more messages; the        first buffer release times with second buffer release times at        which the other audio rendering device releases frames of audio        data from a second buffer of received frames of audio data        maintained by the other audio rendering device.

Embodiment 20: A method, implemented by a pair of audio renderingdevices, the pair comprising a first audio rendering device and a secondaudio rendering device, of synchronising audio content rendered by saidpair of audio rendering devices; the method comprising:

-   receiving, by the first audio rendering device from a wireless    communications device; a first plurality of audio packets, the first    plurality of audio packets including frames of audio data for a    first audio channel from a set of one or more audio channels;-   receiving, by the second audio rendering device from the wireless    communications device; a second plurality of audio packets, the    second plurality of audio packets including frames of audio data for    a second audio channel from said set of one or more audio channels;-   maintaining, by the first audio rendering device, a first buffer of    received frames of audio data and releasing frames of audio data    from said first buffer for rendering at respective first buffer    release times;-   maintaining, by the second audio rendering device, a second buffer    of received frames of audio data and releasing frames of audio data    from said second buffer for rendering at respective second buffer    release times;-   receiving, by the first audio rendering device, one or more messages    from the second audio rendering device; and-   synchronizing, by at least the first audio rendering device, the    first buffer release times with the second buffer release times    based on the received one or more messages.

1. An audio device, comprising: at least one wireless communicationinterface configured to receive a first plurality of audio packets froma wireless communication device, the first plurality of audio packetsincluding frames of audio data for a first audio channel; and aprocessing unit; wherein the audio device is configured to release, atrespective first buffer release times, the frames of the audio data forthe first audio channel from a first buffer for rendering; wherein theaudio device is configured to communicate with an other audio device;and wherein the audio device is configured to synchronize the firstbuffer release times with second buffer release times associated withthe other audio device.
 2. The audio device according to claim 1,wherein the first buffer release times are regularly spaced apart by afirst interval, and wherein the second buffer release times areregularly spaced apart by a second interval equal to the first interval.3. The audio device according to claim 1, wherein the audio device isconfigured to determine first packet receipt times indicative ofrespective times of receipt of audio packets of the first plurality ofaudio packets from the wireless communication device, and to determinethe first buffer release times based on the determined first packetreceipt times.
 4. The audio device according to claim 1, wherein theaudio device is configured to determine at least one of the first bufferrelease times based on a delay interval between a transmission of one ofthe first plurality of audio packets and a transmission of one of asecond plurality of audio packets for the other audio device.
 5. Theaudio device according to claim 4, wherein the audio device isconfigured to release one of the frames of the audio data from the firstbuffer at a time that is equal to a packet receipt time for the one ofthe frames of the audio data in the first plurality of audio packetsdelayed by a buffer delay configured to compensate for the delayinterval.
 6. The audio device according to claim 1, wherein the audiodevice is configured to obtain a message, wherein the message isindicative of a time of receipt, by the other audio device, of aprevious one of a second plurality of audio packets; and wherein theaudio device is configured to determine a delay interval based on (1)the message, and (2) a time of receipt of a previous one of the firstplurality of audio packets by the audio device.
 7. The audio deviceaccording to claim 1, wherein the audio device is configured to obtain amessage, wherein the message is indicative of a sequence number of aframe scheduled for release at the other audio device.
 8. The audiodevice according to claim 1, wherein the audio device is configured toobtain a message, wherein the audio device is configured to maintain thefirst buffer responsive to the message.
 9. The audio device according toclaim 1, wherein the audio device is configured to obtain a message,wherein the message is indicative of an elapsed time since a receipt, bythe other audio device, of a frame of audio data scheduled for releasefrom the a second buffer associated with the other audio device at anext buffer release time.
 10. The audio device according to claim 1,wherein the audio device is configured to obtain a message, wherein themessage is indicative of a buffer depth of a second buffer associatedwith the other audio device.
 11. An audio system comprising the audiodevice of claim 1, and the wireless communication device.
 12. The audiosystem according to claim 11, wherein the wireless communication deviceis configured to transmit the first plurality of audio packets to theaudio device, and to transmit a second plurality of audio packets to theother audio device according to a transmission schedule.
 13. The audiosystem according to claim 12, wherein the wireless communication deviceis configured to transmit each audio packet of the second plurality ofaudio packets to the other audio device at a delay interval after acorresponding audio packet of the first plurality of audio packets istransmitted.
 14. The audio system according to claim 13, wherein theaudio device is configured to determine the delay interval based on amessage received by the audio device.
 15. An audio system comprising theaudio device of claim 1, and the other audio device.
 16. The audiosystem according to claim 15, wherein the other audio device isconfigured to receive a second plurality of audio packets, the secondplurality of audio packets including frames of audio data for a secondaudio channel.
 17. The audio system according to claim 16, wherein theother audio device is configured to release, at the respective secondbuffer release times, the frames of audio data for the second audiochannel from a second buffer for processing.
 18. The audio systemaccording to claim 16, wherein the audio device and the other audiodevice are configured to simultaneous render one of the frames of theaudio data in the first plurality of audio packets for the first audiochannel, and one of the frames of the audio data in the second pluralityof audio packets for the second audio channel.
 19. The audio systemaccording to claim 16, wherein each frame of audio data in the firstplurality of audio packets for the first audio channel has an associatedsequence number, and wherein each frame of audio data in the secondplurality of audio packets for the second audio channel has anassociated sequence number.
 20. The audio system according to claim 19,wherein each frame of audio data in the first plurality of audio packetshas a sequence number equal to a corresponding sequence number of acorresponding one of the frames of audio data in the second plurality ofaudio packets.
 21. The audio device according to claim 1, wherein theaudio device is configured to maintain the first buffer by: selecting abuffer depth of the first buffer; discarding a frame of audio data fromthe first buffer; delaying release of a frame of audio data from thefirst buffer; resetting the first buffer; or one or more of theforegoing.
 22. An audio device; comprising: at least one wirelesscommunication interface configured to receive a first plurality of audiopackets from a wireless communication device, the first plurality ofaudio packets including frames of audio data for a first audio channel,wherein the at least one wireless communication interface is alsoconfigured to communicate with an other audio device, the other audiodevice being configured to receive a second plurality of audio packetsfrom the wireless communication device, the second plurality of audiopackets including frames of audio data for a second audio channel; asignal processor configured to process the frames of audio data includedin the first plurality of audio packets; wherein the audio device isconfigured to release, at respective first buffer release times, theframes of the audio data in the first plurality of audio packets from afirst buffer for rendering; and wherein the audio device is configuredto synchronize the first buffer release times with second buffer releasetimes at which the other audio device releases frames of audio data inthe second plurality of audio packets from a second buffer associatedwith the other audio device.
 23. A method of synchronizing audio contentrendered by a pair of audio devices, the pair of audio devicescomprising a first audio device and a second audio device, the methodcomprising: receiving, by the first audio device, a first plurality ofaudio packets from a wireless communication device, the first pluralityof audio packets including frames of audio data for a first audiochannel; receiving, by the second audio device, a second plurality ofaudio packets from the wireless communication device, the secondplurality of audio packets including frames of audio data for a secondaudio channel; releasing frames of audio data in the first plurality ofaudio packets from a first buffer for rendering at respective firstbuffer release times; releasing frames of audio data in the secondplurality of audio packets from a second buffer for rendering atrespective second buffer release times; and synchronizing, by at leastthe first audio device, the first buffer release times with the secondbuffer release times.